1. Field of the Invention
The present invention relates to a method and apparatus for managing address information utilized in message transmission and reception.
2. Description of the Related Art
In a conventional network system wherein a plurality of branch LANs (Local Area Networks) are connected to each other through a trunk LAN by a plurality of bridge units, when a message is to be transmitted from a station on a predetermined branch LAN to a station on another branch LAN, it is necessary not to transmit this message to branch LANs not associated with message transmission. For this purpose, the message must be transmitted using address information including a pair of a station address of the station on the branch LAN and a bridge port address of an interface of the bridge unit to which this branch LAN is connected. In general, the address pair are registered in an address translation table by a hash method or the like, and when the message is transmitted from the predetermined station to another station by broadcast, or its response message is to be transmitted, the address pair are automatically changed.
Each station of the network system is not always permanently connected to a desired branch LAN and may be connected to the station of another branch LAN upon movement of the station. In this case, the bridge port address associated with the station address is changed. When the address information of the moved station is information prior to movement and registered in the address translation table, the message is transmitted to the branch LAN connected to the station prior to the movement. In this case, a response message is not transmitted from the destination station. In general, when a response message is not received, the same transmission message is repeatedly transmitted. When no response message is received upon a lapse of a predetermined period of time, error processing is performed. If retry or error processing is performed upon movement of the destination station, transmission efficiency of the entire network system is degraded, and a load on the network system is undesirably increased.
When a station is moved in a conventional network system, this station will not be used for a predetermined period of time. A station which does not receive or transmit a message for a predetermined period of time is recognized as a moved station (or failed station), and the address information not utilized for the predetermined period of time is deleted from the address translation table.
According to this conventional method address information associated with a station which is not frequently used in a network system is deleted from the address translation table in addition to the address information associated with the moved station. After deletion of the address information, since a message for this station is transmitted by broadcast, this message is also transmitted to branch LANs not associated with the current message transmission, thus undesirably increasing the load of the network.
Strong demand therefore has arisen for an apparatus capable of transmitting a message to a desired station by utilizing the address information associated with the desired station not subjected to message transmission/reception for the predetermined period of time without immediately deleting this address information from the address translation table.